In view of the large number of products that are now being produced from polymers, there has developed an interest in producing some polymers that can be easily disintegrated or degraded to aid in the waste disposal of the products.
One approach that has been taken in the past has been the formation of polymer/starch composites. The presence of starch in the composites makes the products biodegradable, i.e. the products disintegrate into less bulky materials more readily due to the action of living organisms such as bacteria and fungi upon the starch.
One method which has been used in the past to make such polymer/starch composites has been the blending of the starch with molten polymer, for example in an extruder or mixer. This technique in many cases involves first pretreating the starch to make it more compatible with the polymer. In some cases a prodegradant such as an organometallic compound is also added to the polymer. As the starch is biodegraded the article prepared from such a polymer loses its physical integrity. The article simply falls apart leaving material that is less bulky. When a prodegradant is employed, oxidation of the remaining polymer can result in additional disintegration. The preparation of such polymer/starch composites by blending is difficult and has often been found to be destructive to both the equipment employed and the polymer properties.
Another technique of preparing polymer/starch composites has involved gelling the starch in water and mixing the resulting product with molten polyolefin. This technique often results in a more homogeneous mixture but can result in composites having less than desirable physical properties.
Still another technique that has been proposed for preparing polymer/starch composites involves actually forming the polymer in the presence of starch using soluble transition metal catalysts. Such techniques are disclosed in U.S. Pat. No. 3,704,271 and U.S. Pat. No. 4,431,788. One of the drawbacks of such processes is that the starch has an adverse effect upon the activity of catalysts of the type disclosed in those patents. As a result, it will be noted that the polymer/starch composites disclosed in those two patents do not contain large amounts of polymer. For example, those two patents do not indicate that such processes would be capable of producing polymer/starch composites which contain at least about 80 wt. % or more of polymer.
Since the polymer/starch composites of those two aforementioned patents have relatively large amounts of starch there is obviously a limitation on the extent to which the desirable properties of the polyolefin can be carried forward into the composite. An object of the present invention is to provide a method in which a polymer/starch composite can be prepared which contains a more substantial amount of polymer.
Another object of the present invention is to provide a method for promoting the activity of certain highly active particulate olefin polymerization catalysts.